Revenue from Contracts with Customers (Summary of Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Revenue	$ 34,502	$ 19,940	$ 15,715	$ 79,891	$ 6,451	$ 12,802	$ 15,895	$ 1,636	$ 150,048	$ 36,784	$ 42,877
Research and development services [Member]
Disaggregation Of Revenue [Line Items]
Revenue									1,707	4,150	14,615
License Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue									75,500
Royalty sales milestone [Member]
Disaggregation Of Revenue [Line Items]
Revenue									15,100
Manufacturing services [Member]
Disaggregation Of Revenue [Line Items]
Revenue									3,337
Non-cash royalty revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue									30,424	17,309
Recognition of Deferred Research and Development Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue									22,638	1,325	3,100
Non-cash royalties and milestones [Member]
Disaggregation Of Revenue [Line Items]
Revenue									30,424
License and collaboration milestones [Member]
Disaggregation Of Revenue [Line Items]
Revenue										14,000	24,994
Grant Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue									1,342		168
United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue									149,358	32,784	38,883
United States [Member] | Research and development services [Member]
Disaggregation Of Revenue [Line Items]
Revenue									1,707	4,150	14,615
United States [Member] | License Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue									75,500
United States [Member] | Royalty sales milestone [Member]
Disaggregation Of Revenue [Line Items]
Revenue									15,100
United States [Member] | Manufacturing services [Member]
Disaggregation Of Revenue [Line Items]
Revenue									3,337
United States [Member] | Non-cash royalty revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue										17,309
United States [Member] | Recognition of Deferred Research and Development Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue									22,638	1,325	3,100
United States [Member] | Non-cash royalties and milestones [Member]
Disaggregation Of Revenue [Line Items]
Revenue									30,424
United States [Member] | License and collaboration milestones [Member]
Disaggregation Of Revenue [Line Items]
Revenue										10,000	21,000
United States [Member] | Grant Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue									652		168
Europe [Member]
Disaggregation Of Revenue [Line Items]
Revenue									690	4,000	3,994
Europe [Member] | License and collaboration milestones [Member]
Disaggregation Of Revenue [Line Items]
Revenue										$ 4,000	$ 3,994
Europe [Member] | Grant Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue									$ 690